The present invention relates to frequency agile signal generators and, more particularly, to a method and system for generating signals which emulate complex communication signals and signal environments.
Modern radar and communication systems employ diverse signal frequencies and modulations ranging from relatively common amplitude modulation (AM), frequency modulation (FM), or phase modulation (PM) signals to extremely complex combinations of modulation, frequency hopping, and the like. To provide a realistic environment for test, evaluation, and development of such systems, and to accurately produce such signals for training or other similar purposes, signal generators capable of emulating diverse and complex types of signals are required.
Obviously, a wide range of diverse signals can be produced by individual signal sources, each designed to produce a particular waveform and arranged so that the individual signal generator outputs or combinations thereof can be selected. Of course, such an approach may require considerable hardware filling several equipment racks. As a result, such signal generating systems are expensive, complex to operate and maintain, require considerable space, and lack mobility. Also, an arrangement of individual signal sources has limited versatility and requires the addition of specific signal sources to expand its capabilities.
On the other hand, a single source generator, programmable to provide a variety of signal waveforms and modulation types, typically cannot provide the wide variety of signals encountered in modern radar and communication systems. Thus, signal generators for emulating radar and/or communication signals may use several analog and digital signal sources and may combine and modulate the different signals in a variety of ways to produce a desired output waveform. Even then, however, the equipment may be extensive in size and quite limited in its capability to reproduce modern communications signal formats.
One known approach, exemplified by the CSS-20 series of Communication Signal Simulator available from Lockheed Electronics, provides basic AM, FM, and PM signal channels which can be selected to provide a desired basic generator output waveform. Each channel includes a variety of controls and/or sources to modify the basic modulation so as to provide such capabilities as suppressed carrier (SC) AM, narrowband and wideband FM (NBFM and WBFM), and a variety of pulse modulations such as pulse width modulation (PWM), pulse amplitude modulation (PAM), pulse position modulation (PPM), and the like. Simulation of modern communication systems, however, requires far greater variety of signal waveforms and modulation characteristics. Moreover, there is a need for very fine, dynamic control of signal parameters over a wide range of variation yet with a capability characterized by speed and ease of parameter selection.